In-Floor Radiant Hot Water Heat

[Mac88]

We've been looking for new digs and have come across a lot of properties in our price range built on slab, with no basement. Anyone here have experience with installing in-floor radiant hot water heating "after the fact", over a concrete slab? I haven't been able to find much information. I know it will entail laying down stringers and some type of overlayment to protect the heating coils (tubing). We're looking at an indoor wood fired boiler as the heat source. Radiate floors run relatively cool compared to baseboard or radiators. I'm not sure how to make that happen. Since it's a closed loop, you can't modulate it by mixing cold water. Any thoughts, ideas, or experience with something like this?

 

[stihl023/5]

We've been looking for new digs and have come across a lot of properties in our price range built on slab, with no basement. Anyone here have experience with installing in-floor radiant hot water heating "after the fact", over a concrete slab? I haven't been able to find much information. I know it will entail laying down stringers and some type of overlayment to protect the heating coils (tubing). We're looking at an indoor wood fired boiler as the heat source. Radiate floors run relatively cool compared to baseboard or radiators. I'm not sure how to make that happen. Since it's a closed loop, you can't modulate it by mixing cold water. Any thoughts, ideas, or experience with something like this?

Indoor wood fired boiler with no basement?:confused2:

 

[JHctRednek]

Installing radiant on a slab is very similar to installing radiant with a tile floor, lay a hardi back type of board down with the radiant loops in it and sheath over the top with regular ply.

Is there gonna be a regular oil boiler as a backup?

With a regular boiler the water circulating to the radiant is on a separate zone and flows thru a modulating valve.

If there are no controls on the indoor wood boiler to control temperature. You could add some kind of "dump zone" with a mixing valve to drop the water temp.

When I used to run my wood stove with coils in it, the water circulated to the hot water tank, I had a couple large cast iron steam radiators in the garage to cool the water if it got too hot in the wood stove for the water heater. I ended up adding another large radiator in the basement as well cause the water was getting to hot all the time in the dead of winter.

Best of luck

 

[tld400]

We've been looking for new digs and have come across a lot of properties in our price range built on slab, with no basement. Anyone here have experience with installing in-floor radiant hot water heating "after the fact", over a concrete slab? I haven't been able to find much information. I know it will entail laying down stringers and some type of overlayment to protect the heating coils (tubing). We're looking at an indoor wood fired boiler as the heat source. Radiate floors run relatively cool compared to baseboard or radiators. I'm not sure how to make that happen. Since it's a closed loop, you can't modulate it by mixing cold water. Any thoughts, ideas, or experience with something like this?

Instead of putting the radiant hot water heat in the floors you could put it in the walls.

 

[Mac88]

Indoor wood fired boiler with no basement?:confused2:

Sure. You're heating water rather than the air.

Installing radiant on a slab is very similar to installing radiant with a tile floor, lay a hardi back type of board down with the radiant loops in it and sheath over the top with regular ply.

Is there gonna be a regular oil boiler as a backup?

With a regular boiler the water circulating to the radiant is on a separate zone and flows thru a modulating valve.

If there are no controls on the indoor wood boiler to control temperature. You could add some kind of "dump zone" with a mixing valve to drop the water temp.

When I used to run my wood stove with coils in it, the water circulated to the hot water tank, I had a couple large cast iron steam radiators in the garage to cool the water if it got too hot in the wood stove for the water heater. I ended up adding another large radiator in the basement as well cause the water was getting to hot all the time in the dead of winter.

Best of luck

One of my concerns is moisture incursion (weeping) into the overlayment.
If we get something with an attached or nearby, uninsulated, garage we could use that as a heat dump. Whether that would be sufficient would depend on outdoor temperature. I'm trying to keep it as un-complicated as possible.
Not planning on a backup boiler. We would have a wood stove and/or cook stove, like we do currently.

Instead of putting the radiant hot water heat in the floors you could put it in the walls.

I think in cold climates slabs tend to get cold since they'e exposed around the edges, and aren't (usually) insulated. Putting the heat IN the walls would probably be more invasive, and require working around plumbing, wiring, and so forth.

Thanks for your input and ideas. All food for thought.

 

[tld400]

Sure. You're heating water rather than the air.



One of my concerns is moisture incursion (weeping) into the overlayment.
If we get something with an attached or nearby, uninsulated, garage we could use that as a heat dump. Whether that would be sufficient would depend on outdoor temperature. I'm trying to keep it as un-complicated as possible.
Not planning on a backup boiler. We would have a wood stove and/or cook stove, like we do currently.



I think in cold climates slabs tend to get cold since they'e exposed around the edges, and aren't (usually) insulated. Putting the heat IN the walls would probably be more invasive, and require working around plumbing, wiring, and so forth.

Thanks for your input and ideas. All food for thought.

I have a 2000 sq ft ranch on a slab with one wood stove in the front of the house and I use a fan to blow the hot air to the back of the house. Floors are all tile except for my bedroom and house stays real warm. Instead of trying to use pipeing through floor you could just use the wire kits they have out. The wire goes down and you just pore that leveling concrete over it. Heat whole house like you do with stove and put floor heat on for the real cold nights when you want to. I dont think they use alot of electric.

 

[brenndatomu]

Somewhere I seen a system made for this application. It was basically plywood or something that had channels routed in it, you just snapped the pex line in it at whatever spacing you wanted. I'll see if I can find it again.

 

[wndwlkr]

You might look here The Best Overall Radiant Heating Sytems they may have some ideas.

 

[Guswhit]

We supplied the material for a new home construction 2 years ago and the owner planned for radiant heat on the first floor. The used an extra 2x4 plate when building the house walls to raise them up and then floated in 1 1/2" of gyp crete after the tubes were attached to the subflooring. Now I know that this you do not have this luxury, but maybe the gyp crete would adhere to the existing concrete or a binder additive could be applied to get it to stick. Sounds like a large undertaking. Good luck.

 

[Marc]

Somewhere I seen a system made for this application. It was basically plywood or something that had channels routed in it, you just snapped the pex line in it at whatever spacing you wanted. I'll see if I can find it again.

Thinking of Wirsbo Quick Trak?

I put this in a bathroom under tile and it works great! The only minor downside is it uses an odd size tubing, 5/16" dia, but adapter fittings can be had if you know where to look. I got all my stuff from PexSupply.com.

You run the tubes in the channels with an adhesive/thermal gel (using a caulking gun). I put the backerboard right over it and tiled as normal. You just want to be really careful how you attach your flooring over it so as not to puncture.

And Mac88, I have an oil boiler, but the temperature issue was the same as if I had a wood fired boiler, which I might in the future. Also was an issue because I only had the one radiant zone and cast iron radiators everywhere else running at typical boiler temps, 160-180F.

What you do is put a thermostatic mixing valve in the loop before the zone's circulator, with the output going to the loop, the cold coming from a tee in the return line and the hot coming from the boiler. Set the mixing valve to whatever target temperature you want your floor, based on comfort, target room temp and heat loss estimate. It doesn't have to be perferct and you can mess with it until you get it where you want it. Generally I try and have the water circulating all the time in the winter to keep the floor at a consistent temperature.

 

[brenndatomu]

Thinking of Wirsbo Quick Trak?

I put this in a bathroom under tile and it works great! The only minor downside is it uses an odd size tubing, 5/16" dia, but adapter fittings can be had if you know where to look. I got all my stuff from PexSupply.com.

You run the tubes in the channels with an adhesive/thermal gel (using a caulking gun). I put the backerboard right over it and tiled as normal. You just want to be really careful how you attach your flooring over it so as not to puncture.

And Mac88, I have an oil boiler, but the temperature issue was the same as if I had a wood fired boiler, which I might in the future. Also was an issue because I only had the one radiant zone and cast iron radiators everywhere else running at typical boiler temps, 160-180F.

What you do is put a thermostatic mixing valve in the loop before the zone's circulator, with the output going to the loop, the cold coming from a tee in the return line and the hot coming from the boiler. Set the mixing valve to whatever target temperature you want your floor, based on comfort, target room temp and heat loss estimate. It doesn't have to be perferct and you can mess with it until you get it where you want it. Generally I try and have the water circulating all the time in the winter to keep the floor at a consistent temperature.

Yeah, that's it, I'm not sure it was that brand, but basically the same product.

 

[JHctRednek]

Good explanation Marc.

I was asking about the back up boiler for the temperature control. Some of the indoor wood boilers I have seen have a great fluctuation in temp (140 to almost 200) which would be hard to control with a mixing valve. If the indoor wood boiler has good control (160-180) I agree a mixing valve should suffice. A modulating valve is more complex as it senses down stream temp in the floor and opens and closes independent of the zone valve to regulate floor temp. With this system the wall thermometer opens and closes the zone valve and the modulating valve opens and closes to maintain the floor at a set temp.

Best of luck

 

[bing]

I cant' help you with details, but I have a buddy who runs a crew that pumps gypcrete over radiant coils in new apartment buildings. This might be something to look into.

 

[Marc]

Huh, I wasn't aware mixing valves had such a limitations. I thought most of them were pretty quick responding since they're rated for antiscalding applications and such.

I briefly looked at the specs of my Taco valve and it only specifies a minimum temperature difference between the hot side and outlet of 20F and a max inlet temp of 210F...

 

[JHctRednek]

Huh, I wasn't aware mixing valves had such a limitations. I thought most of them were pretty quick responding since they're rated for antiscalding applications and such.

I briefly looked at the specs of my Taco valve and it only specifies a minimum temperature difference between the hot side and outlet of 20F and a max inlet temp of 210F...

I guess its a performance issue more than a limitation with mixing valves (tempering valves). They are designed around a fluctuating inlet temperature of 20 degrees because most boilers are set this way (160-180, with the exception of the newer triple pass boiler with cold start capability but they usually have indirect water heater). With a wider inlet temperature band say 50 degrees the valve cannot open enough to allow propper operating temp, in terms of hot water the temp would not exceed 120 dergees so no one is getting hurt. I have seen this in peoples houses who turn the low side on the boiler down to 120 degreees to "save" on oil and then call a service man because they don't have enough hot water.

Also with a mixing valve installed in a radiant system when the exterior temp gets really low you have to adjust the valve to make up for the additional lost heat. For example my folk's house has radiant in the kitchen and bathrooms but still had general heating equipment (baseboards and kicker heaters) in all other areas. In this situation a mixing valve works ok the rooms stay warm and the general ambiance of the house is good from 40 degree weather to 0 degree weather, this is because the general heating equipment keeps up with the extra lost heat when its really cold out. On the other hand when we converted a garage to an inlaw appartment and installed radiant in all rooms on two zones with a mixing valve in each zone when the temps dropped in the 30s you had to adjust the mixing valve to keep the appt warm. This was because the appt lost more heat than the radiant could supply. Additionally we added a bypass feature for one of the zones because the mixing valve couldn't keep up when the temps were in the teens. The next year we replaced the mixing valve with a modulating valve on one zone and all issues went away. The second zone got a modulating valve and everything was good.

I guess if MAC88 doesn't mind fiddling with mixing valves and live in an area with mild winters then a mixing valve would work fine in a house with radiant as its sole heating source. If he wants to "set it and forget it" go with a modulating valve.

I should preface this with the fact that I have never directly piped an indoor wood boiler to a radiant system. When we had an indoor wood boiler its damper was controlled by the oil boiler and maintained 160-180 temps and now with our outdoor wood boiler we use plate heat exchangers and utilize the boiler controls for radiant zones.

Best of luck

 

[stihly dan]

First thing is you must insulate the slab 1st. Don' let it rob the btu's. 2nd, flate plate heat exchanger, for the floor temps, and a solar/electric hot water heater. Heated by boiler. Lastly, is this going to be in maine?

 

[Mac88]

Thanks guys. Lots of good info and ideas presented here. I'll have to take some time and digest it all, along with doing some more research using your info.

Lastly, is this going to be in maine?

Yup...not cast in stone, but we're looking at what's available. I'm not really interested in refurbing a 200 year old farmhouse. ;o)

 

[stihly dan]

We would welcome you back here in the north east. Boiler is going to be a gasifier of course.

 

[Mac88]

We would welcome you back here in the north east. Boiler is going to be a gasifier of course.

Probably. We're looking at what's available. North east would probably be north of the 45th parallel, with lots of woods. :msp_biggrin:

 

[stihly dan]

May have to bring a trailer of that hedge with ya. Help make friends with the neighbors.